1. Field of the Invention
The present invention is generally directed to the field of railroad rolling stock hot bearing detection and, in particular, to an improved system for insuring that hot bearing detectors are operating properly.
2. Description of the Related Art
Defective wheel bearings on railroad equipment are a particularly important problem. When the maximum operating temperature of a railroad wheel bearing is exceeded, the wheel may fail, thus causing a derailment. Derailments, in addition to being hazardous to crews and passengers, may also lead to the contamination of the environment due to the spilling of hazardous materials and the like. In order to eliminate and minimize derailments, railroads typically employ "hot bearing detectors".
Hot bearing detectors, also known as "hot box detectors," are commonly used on railroads. The detectors include heat sensing scanners which are located at designated points along railroad tracks. The scanners sense the temperature of bearings on passing railroad rolling stock and, typically, transmit the sensed temperature information to a telemetry unit. At the telemetry unit, the sensed bearing temperature is compared against a reference and, if the reference temperature is exceeded, an alarm is transmitted via the telemetry unit to the locomotive engineer or a control tower.
The detectors are usually optical pyrometers aimed at the wheel bearings to detect excessive heat. A detector is typically aimed vertically at an angle with respect to the ground, so that it measures the thermal radiation from a bearing on the near side of the car. The thermal radiation measured is converted to a temperature reading.
Frequently, the detectors are activated by magnetic sensing transducers mounted near the rail which are triggered by the metal of the passing wheel flange. The magnetic sensors can be located near the detector location to activate the detector as each wheel passes, or the sensors can be located to activate the detector for the entire duration of a train and deactivate the detector after the train has passed. Detectors can be located on either side of a track.
When a hot box detector signals an over-heated wheel bearing, the locomotive engineer is expected to stop the train and determine whether the bearing is indeed over-heated. The stoppage of railroad traffic for this reason results in downtime for both freight and passengers. Accordingly, it is important that train stoppages for defective wheel bearings take place only when a defective wheel bearing condition has actually occurred. Conversely, it is important that all hot box detectors along a railroads' trackage be operating properly. Defectively operating hot box detectors may permit trains having defective wheel bearings to proceed uninterrupted thus causing derailments and corresponding injuries and property damage.
Verification and maintenance of hot box detectors is typically carried out by railroad employees who travel along the track periodically and who stop to verify hot box detectors along the route. Such maintenance and calibration procedures are labor intensive and expensive. More importantly, however, maintenance personnel are able to check hot box detectors only under static conditions. Hot box detectors may appear to be operating properly under static conditions but may, in fact, fail to detect hot wheel bearings under the dynamic conditions created by passing trains.
Hot box detectors typically fall into two classes, namely rail-mount and ballast-mount types. Rail-mounted hot box detectors are mounted on the ties directly next to the rail of a railroad track. Ballast mounted hot box detectors are located in the ballast adjacent the rail. The accuracy of both types may be affected by the passage of a train along the rail. For this reason, dynamic testing of hot box detectors is desirable.
It is desirable to provide an apparatus for maintaining and verifying hot box detectors which monitors the operation of such detectors under dynamic conditions caused by the passage of a load along the railroad track.
U.S. Pat. Nos. 4,878,437 and 4,974,797, both to Myers et al., show dynamic hot bearing simulators. The Myers et al. simulators include two heaters near each of several bearings. The heaters simulate bearings having specified temperatures above ambient to verify operation of hot box detectors. Because the heaters are mounted near the wheels, they must be mounted on the trucks to avoid interfering with relative movement of the carriage and trucks. In practice, mounting hardware has loosened or failed due to vibration of the trucks. In addition, such systems require a heater on each side of a bearing so that a leading detector senses one heater and a trailing detector senses the other. Because the location of the heaters interferes with detection of a hot box on the car equipped with the simulators, the car must be equipped with an on-board hot box detector safety system such as temperature transducers mounted on the bearing housing.